3 Answers
3

Finger picks are used as a preference. Players such as Chet Atkins had a very famous style of picking, where he mainly used a thumb pick I believe (check out Stairway to Heaven by Hayseed Dixie, Mr Sandman by Chet Atkins) Players like Jeff Beck use their fingers mainly, which he has developed a neat playig style. Then about everyone else uses a pick, because it's probably the easiest. So it all depends on your preferences / what you're playing. You could also use your pick and fingers at the same time, and that is done by holding the pick between your thumb and index finger and then using the other three to pluck the strings.

"Players like Jeff Beck use their fingers mainly". Beck used a pick for years and years, but was adept with his fingers. According to an interview with him, he said he dropped the pick during a concert one night and finished a song without it and decided he wasn't going to bother with it. But, then again, he's Jeff Beck.
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AnonymousMar 4 '11 at 5:04

The benefit of using a pick is a louder attack, which is really important when you're purely unamplified and near other, often louder instruments, and where the attack of the note is crucial. Dobro and banjo players are really top ones here, and I understand it's big for pedal steel players.

Classical and flamenco players pick with fingernails, but nylon strings are easier on fingernails than steel strings. I've heard fingerstyle players talk about superglueing slivers of ping pong balls to their fingernails to have something replaceable and more able to withstand the strings, yet more stable on the finger than fingerpicks.

There are players who just use a thumbpick. Nils Lofgren plays rock with a thumbpick and fingers. With electrical playing, especially rock playing, it seems like the benefits of fingerpicks are not more easily handled by amplification. For hybrid playing, picks are allowed but not necessary.

Fingerpicks are used instead of fingernails. I don't think many (or any) classical guitarists use them, but some steelstring guitar players do(blues/bluegrass). Fingerpicks are basically used to get that nail type sound without destroying your nails. As you see on many classical guitarists they have very long nails, sometimes fakenails, which allow them to get a differnet sound. Fingerpicks could be used to get somewhat the same sound...(a bit too general)

As you are more into mainstream music I would suggest putting down the fingerpicks and use your fingers or a pick instead.